This invention relates to a navigation system for a vehicle, which system guides the vehicle along a route from a staring place to a destination by displaying a direction for the vehicle to follow.
According to this system, when the vehicle is travelling straight ahead, as shown in FIG. 6(A), a straight arrow is displayed on a display unit. When the vehicle reaches the point where it must take some action such as change its direction (hereinafter called "a turning point"), such as an intersection where it must turn right or left, a right turn arrow or left turn arrow is displayed as shown in FIGS. 6(B) and 6(C). Therefore, the system guides the vehicle so that it travels on a predetermined route from the starting place to the destination. This technique is disclosed in, for example, Japanese Laid-open Patent Publication No. 60-200399.
The route from the starting place to the destination may be predetermined manually, leg by leg. Generally, however, when the starting place and the destination are entered, the navigation system computes the route from geographic information contained in a map database.
As shown in FIGS. 6(A), 6(B) and 6(C), the navigation system of the prior art displays a direction of advance for a single place only, that is, for straight ahead or for the next turning point. Until the vehicle passes the first turning point, there is no display of the direction of advance for a second and subsequent turning point, where the vehicle must change its direction again. Therefore, if two intersections that are turning points are dose together, the unalerted driver may pass the second turning point without sufficient advance warning to change direction. Further, if the road curves sharply after the first turning point, the driver will not see the sharp curve until he passes through the turning point. Such lack of warning is incompatible with safe driving.